Short notes from my readings.
We all know that earth is a spherical, it has been taught to us since our childhood. The notion is so common that we somehow suppress our original thought, when we observe outside, that earth could be flat.
That brings an interesting question on how and when did human first come to realize that earth is not flat. Mere observation may not help as when we see around us, both cities and plains, that land we see is infinitely flat. Occasionally, when we look at the mountains, we observe the land going up and then coming down, it is the same, but in the reverse order when we observe it in the valley. If we iron out these oddities, we still land up on the same conclusion that earth could be flat.
However, careful observation and thinking by looking at the mountain, could help us derive at a different conclusion. If we look up the mountain, we see a smooth line of the earth and the sky touching. If the earth were flat, than that smooth line could be considered the boundary, in other words, horizon of the surface denoted by that horizontal line. But, if we venture past that mountain top, we know that that is not end as we saw from the bottom, but there is a slope down and then mountain was curved surfaced which looked horizontal to our eyes.
The same analogy could be drawn to a ship on the surface of an ocean and if we see a ship on the horizon, it slowly goes down the other side, little by little and never jumps off the cliff. This can help us derive that earth is not just flat, but it is a curved surface.
And we see this phenomenon throughout the ocean surfaces, which makes us believe that earth's curvature is uniform, in other words, spherical.
This kind of reason was first explained by pythogoras in 500 BC. Later in 340 BC, Aristotle settled this matter once and for all by providing numerous examples. Like, when observing lunar eclipse, when earth cast it's shadow on moon and we can observe that earth's surface is curved.
Modern world does not need much proof, we have photos of earth captured from space, which asserts that pythagoros guided the human thinking in the correct direction.